There has recently been an increasing demand for automatic lathes provided with a turret device that can be fitted with a plurality of tools so as to cope with a need for adopting to a large variety and small quantity manufacturing system while effecting automation as well as speedup of machining operation.
The turret device is structured such that a turret mounted on a tool rest main body is capable of executing indexing rotations so as to present any of normally 5 to 12 indexing positions optionally. Tool mounting portions are formed on a peripheral face or an outer end face of the turret, and various tools such as a turning tool, a drill, and so forth can be mounted on the respective tool mounting portions, enabling automatic selection of suitable tools according to the content of a machining operation through indexing rotations of the turret.
A pair of coupling members capable of engaging with each other and disengaging from each other (clamping/unclamping) are provided between the tool rest main body and the turret, and the turret can be rendered freely rotatable or fixedly held for positioning in a given indexing position by engaging the pair of the coupling members with each other or disengaging the same from each other.
For the coupling members described above, coupling members in the form of crown gears of a curvic coupling or the like for being meshed with each other are generally adopted.
With this type of the coupling members, engagement and disengagement thereof are normally effected by moving a coupling member disposed on the turret side in the axial direction relative to a coupling member disposed on the side of the tool rest main body. More specifically, for effecting the indexing rotation of the turret, engagement between the respective coupling members is released by moving the turret in the axial direction relative to the tool rest main body, and while the respective coupling members are kept in this state, the indexing rotation of the turret is executed.
The indexing rotation of the turret is executed subsequently to completion of a machining operation with the use of a certain tool. Accordingly, a workpiece and a main spindle table for supporting the workpiece are present in the vicinity of the turret at the time of the indexing rotation.
Hence, if the indexing rotation of the turret is executed with the turret kept in a position where it is present upon completion of the machining operation, this involves a risk of the turret and a tool fitted to the turret coming to interfere with the main spindle table and the workpiece as a result of a movement of the turret in the axial direction.
Accordingly, it has been conventionally necessary to carry out programming for a machining operation such that the indexing rotation of the turret is executed after the turret device is moved to a position where such interference can be avoided.
Such programming for a machining operation needs to be carried out by a user himself according to the content of the machining operation. A machining program to be inputted in an automatic lathe is generally developed by a user while referring to a design drawing of a product.
However, the movement of the turret in the axial direction accompanying the indexing rotation thereof can not be known from the design drawing of the product, because the movement is a motion depending on a structure of the automatic lathe. Accordingly, it has been troublesome for the user to develop a machining program always taking into account a distance of the movement. Furthermore, there has been a risk of the user's making a mistake of developing a machining program without taking into account the movement of the turret in the axial direction associated with the indexing rotation. In case of such a mistake being made, there is a possibility of the turret and tools coming to interfere with the main spindle table and the workpiece, thereby destroying the latter.
In addition, if the turret device is caused to make an evacuating motion every time when the indexing rotation of the turret is executed, this will result in a longer machining time by at least the length of time taken for making the motion.
In the light of such circumstances as described, the present invention has been developed, and an object of the invention is to prevent the turret and a tool fitted thereto from interfering with the main spindle table and the work, and to shorten machining time by eliminating the movement of the turret relative to a lathe main body on which the main spindle table is mounted during the indexing rotations of the turret while simplifying programming by the user for a machining operation.